Multi-site communication systems provide wide-area coverage for users of the system. These systems comprise a number of sites, with each site corresponding to a different geographic coverage area and each site having located therein an infrastructure device (which will hereinafter be referred to as a repeater) serving the coverage area by managing one or more channels (e.g., uplink and downlink channels, time slots, radio frequency channels, etc.) in the coverage area. Accordingly, for purposes of the teachings herein, a site is characterized by a repeater that serves a particular coverage area, a channel for wireless communication device transmissions, and a system identification that identifies transmissions from the repeater on the channel at the site. Some or all of the infrastructure devices in a multi-site communication system may be networked or connected together to provide the wide-area coverage, and in many instances two or more of the coverage areas have some degree of overlap.
Multi-site communication systems may be designed as trunked systems or conventional systems. In trunked systems, a limited number of communication channels are shared among a much larger number of users to facilitate efficient use of the system's communication resources. Thus, to afford each user a reasonable opportunity to use the system's resources, one or more control channels are utilized by the infrastructure to allocate the shared resources between the many users in the system. In general, when a wireless communication device (which will hereinafter be referred to as a radio) wants to communicate on the trunked system, it sends a request on the control channel to communicate with another radio or group of radios. In turn, the requesting radio (and the radios to which it desires to communicate) receives back on the control channel the allocation of a traffic channel to use for their communications. Upon the conclusion of the communications, the allocated channel is released for use by other radios in the system.
In conventional systems, a number of communication channels are also shared amongst a number of users (although the number of users per channel is typically much smaller than in trunked systems). However, there is no control mechanism provisioned in the infrastructure to allocate the resources among the users in the system. Thus, in contrast to a trunked system, each channel in a conventional system is dedicated to one or more groups of users enabling the users to control access to the channels through their radios by manually selecting a channel or selecting a talkgroup that is assigned a particular channel.
As a user roams or travels in a multi-site communication system, the user may move from one coverage area served by one repeater of which it is aware to a new coverage area served by a different repeater of which it may not be aware. In that case, the user's radio must be able to detect the repeater in the new coverage area to facilitate communications in that coverage area. In trunked systems, naturally, the control channels can be used to help radios locate a repeater. More particularly, the repeaters periodically send out a message on the control channel that identifies the repeater (e.g., via the system identification) and that provides addressing for contacting the repeater. Moreover, the repeaters in trunked systems are generally continuously keyed, which helps to locate a repeater, and some repeaters transmit adjacent site information that can assist a radio in finding a suitable repeater.
Conventional systems do not use control channels to locate a repeater upon a radio moving to a new coverage area. However, in some conventional systems, the repeaters periodically broadcast beacon messages that serve the same purpose as the messages sent on the control channel in that they identify the repeater and provide contact information for the repeater. However, the transmission of beacon messages is not allowed in all conventional communication systems for various reasons including transmission regulations.
An alternative manual method could be used to find a repeater in a conventional system, which involves a user manually tuning his radio in an attempt to locate the repeater for the coverage area in which he is currently located. As might be expected, this approach can be cumbersome, time consuming, and not the most effective method of finding the repeater that provides the radio with the best signal strength for transmitting and receiving the radio's communications. In addition, some conventional systems require the repeater to de-key or enter into an inactive sleep mode when there have been no transmissions on its channel(s) for a certain length of time. This can further exacerbate the problem of a radio locating the repeater upon entering the repeater's coverage area, especially if there happens to be a relatively lengthy time until the next transmission by the repeater on the channel.
Thus, there exists a need for a method for site selection by a radio in a multi-site communication system that can be used in conventional multi-site communication systems.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of various embodiments. In addition, the description and drawings do not necessarily require the order illustrated. Apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the various embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Thus, it will be appreciated that for simplicity and clarity of illustration, common and well-understood elements that are useful or necessary in a commercially feasible embodiment may not be depicted in order to facilitate a less obstructed view of these various embodiments.